class_docstr: Write values to mask of zero-initialized array
class_docstr_tok: ["Write","values","to","mask","of","zero-initialized","array"]
code: def backward(self, indices, grad_outputs):
      (g,) = grad_outputs
      return (g[self.mask],)
  
file_path: chainer/chainer/functions/normalization/l2_normalization.py
imports: import six
  from chainer import backend
  from chainer import function_node
  import chainer.functions
  from chainer import utils
  from chainer.utils import type_check
label_desc: Use image node_id 3 for calling the _SetItemZero obj's underlying member method code with example usage: obj.backward(indices, grad_outputs) and returns: g